Measurement of cardiac output and "central" blood volume by various systems

¹ Mayo Clinic and Mayo Foundation, Rochester, Minnesota

Dilution curves were obtained by sampling from the aortic root or a carotid artery after injection of indicator dye into the pulmonary artery in five dogs at rest and during exercise. On four occasions a common sampling system was used; curves were recorded simultaneously and in parallel from a cuvette oximeter assembly with a slow dynamic response and from a phototube densitometer with a fast response. In the fifth study, separate slow and fast sampling systems were used interchangeably with the two detecting instruments. Values for cardiac output were similar with the two instruments; maximal divergence for any single observation was 9% from the line of identity. The aortic root is a favorable sampling site for such a comparison, since extrapolation of the dilution curves is usually unnecessary. Under these conditions measurement of cardiac output was not influenced by the dynamic response characteristics of the sampling-detecting-recording system. When mean transit times of the respective curves were corrected for instrumental delay, there was also satisfactory agreement in values for "central" blood volume. However, since the time correction for the densitometer is relatively small, it is the preferable instrument for this measurement.